The disclosure of Japanese Patent Application No. HEI 10-263348 filed on Sep. 17, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an art for assisting an operator in carrying heavy articles, with which an operator is able to carry heavy articles using an assist device while feeling as if he were carrying a light article.
2. Description of the Related Art
Many attempts have been made for the realization of the above-mentioned art. An example is disclosed in xe2x80x9cControl of Man-Machine System Based on Virtual Tool Dynamics xe2x80x9d (Kazuhiro KOSUGE, Yoshio FUJISAWA and Toshio FUKUDA, Transactions of the Japan Society of Mechanical Engineers, Series C, Vol. 60, No. 572 (1994-4) pp. 211-217). It is reported, that when the actuator output is controlled by a human in a robot cooperation system so that the equation,
Mv d2x/dt2+Dv dx/dt+Kv x=Q Fhxe2x88x92Fe
is satisfied, when an operator is working in cooperation with a robot, the operator is able to perform the work as if he were using a tool for amplifying the operating force of such tools as a nail puller, a pair of pincers, and a wrench. In the above equation, Mv is the mass matrix of a virtual tool, Dv is the matrix of viscosity coefficient, and Kv is the spring constant matrix, each being an nxc3x97n matrix. Q is the magnification for amplifying the force of an operator, Fh is the operating force of the operator, Fe is the force applied to an object article by a manipulator, and x is the position of the object article. Further, Mv, Dv, and Kv are values determined based on the characteristics of tools equivalent to the robot from the standpoint of an operator.
In the art xe2x80x9cMotion Generation of Robot in Cooperation with Humanxe2x80x9d (Kazuhiro KOSUGE and Norihide KAZAMURA) in Transactions of the Fifteenth Japan Robot Society Sessions, pp. 393-394, there is disclosed a carrying system wherein human and robot cooperate to carry articles, an actuator output is controlled so that the equation,
Mv d2x/dt2+Dv dx/dt+Kv x=Fh
is satisfied. Further, the values of Mv, Dv, Kv, and the like were varied to experimentally confirm the change in operability in a system where human and robot cooperate to carry articles. According to the results thus reported, it is easier to carry the articles smoothly when a larger coefficient for acceleration d2x/dt2 (mass matrix Mv of the virtual tool) is taken (referred to as an impedance control), and it is easier to move the articles by small notches when a larger coefficient for speed dx/dt (matrix of viscosity coefficient Dv) is taken (referred to as damping control). Conversely, it is reported that it is difficult to move the articles in small notches during impedance control and that it is difficult to move the articles smoothly and substantially linearly during damping control. It is further reported that the mass matrix Mv and the matrix of viscosity coefficient Dv needs to be adjusted to proper values depending on the type of cooperation work conducted. Also, the spring constant matrix Kv is set to 0 in the report, because a spring force, which changes according to the position, ordinarily does not act when carrying an article. However, the spring constant matrix Kv cannot be set to 0 when carrying an article subject to spring force and therefore, it can be easily apprehended that there exists an appropriate value for spring constant matrix Kv for providing a good operability.
A series of papers described above report a realization of good-quality work, without giving an operator a disagreeable feeling, by providing a behavior equivalent to that when force amplification tool such as a nail puller is employed by using an assist force of a robot. Also, it is reported that a tool capable of realizing equivalent characteristics depending on the type of work needs to be selected, so that casually selecting the mass matrix Mv, matrix of viscosity coefficient Dv, spring constant matrix Kv, and the like leads to working with inappropriate tool for intended work. This results in difficulty of accurately positioning an article at a target position after carrying the article smoothly near the target position, in the case of carrying the articles. The locus of the article until it is carried near the target position tends to be zigzag rather than a smooth line. Accordingly, it is reported that it is necessary to change the control method for the assist force needs to be changed.
xe2x80x9cExperimental Evaluation for a Robot Carrying an Object with a Humanxe2x80x9d (Ryojun IKEURA, Haruaki KOZAWA and Kazuki MIZUTANI, Japan Society of Mechanical Engineers No. 98-4 Robotics-Mecbatronics Sessions 98 Transactions 2AIII-3(1) to (2) ) discloses a recognition that it is necessary to change the viscosity coefficient (described as damping coefficient) established between the operating force of an operator and the speed of the article during a work to construct a cooperation system free from disagreeableness. To this end, a method for altering the viscosity coefficient according to the time lapsed from the start is proposed by this paper.
The first and the second papers described earlier indicate important views in constructing a cooperation system that does not make an operator feel disagreeable, and have made great achievements. However, because the system stands on the ground of using an equivalent tool, no consideration is made as to the view corresponding to exchange of tools during a series of work.
In the third paper mentioned earlier, changing of the viscosity coefficient according to time lapsed is discussed, which almost corresponds to sequentially changing tools during work. However, there is no general consideration as to what characteristics to give to what work. Further, because the analysis result is based on only one type of work, it contains no information on how to change the mechanical properties of the assist device when the content of work is changed. Further, the object to be changed timewise is limited to the viscosity coefficient (equivalent to mass) and therefore the proportional coefficient established between the acceleration and force proportional to acceleration is not considered.
The present invention has been made to improve the state of the art, and it makes a new proposal for how to change the mechanical properties during a series of work.
It was also found that it is necessary that an operator feels appropriate reaction force in realizing the aforementioned good work, and still further, it is necessary to change the reaction force pattern required by the operator according to the content of work, task process phase, operator, work duration, experience, state of fatigue of the operator, and the like. Therefore, another object of the present invention is to realize a work assist device which satisfies such requirements.
According to a first aspect of the present invention, the work assist device includes a movable body for supporting heavy articles, an actuator for actuating the movable body, and a controller for controlling the output of the actuator. The controller controls the output of the actuator such that the relationship between the force applied to the movable body by the operator and the movement of the heavy article realized through the movement of the movable body is equivalent to the relationship between the force generated by application of the equivalent force to a virtual article placed in a free space and which is lighter than the heavy article and the movement created thereby. Further, the controller adjusts the actuator output such that the equivalent mass of the virtual article fluctuate during a series of carrying work.
According to the first aspect, the output of the actuator is adjusted when an operator applies operating force to the movable body. Then, the operating force of the operator (referred to as reaction force) together with the output from the actuator creates movement of the heavy article through the movable body. The output from the actuator is adjusted such that the movement of the heavy article realized at this point is equal to the movement realized when the same operating force is applied to a lighter article without any assist force. Further, the output from the actuator is adjusted such that the heavy article moves as if the weight or the mass of the lighter article (referred to as the virtual article because it does not exist) fluctuated during a series of movement. From the standpoint of the operator, this means that the operator performs the work with the operating force required when dealing with an object article whose weight or mass fluctuates.
It was confirmed by experiment that a good-quality work is easy to realize when the output of the actuator is adjusted such that the force required of the operator is the force required when the weight or mass of the virtual article (referred to as equivalent mass) changes. That is, the operator is able to perform work with reaction force (or resistance) most convenient for the work during a series of work. The operator is able to work with appropriate reaction forces when dynamically and smoothly moving an article or when accurately moving an article by a small amount, resulting in a movement intended by the operator.
Further, it was found by a series of experiments that carrying of articles can be classified into several movement phases. When an article is carried by an operator, the article goes through a speed increase period after start and to a speed decrease period, and then it is positioned at a target position while being decelerated. In detail, the period of speed increase can be classified into two phases, prophase wherein the absolute value of acceleration increases and anaphase wherein the absolute value of acceleration decreases. Further, it was confirmed that the speed decrease period can also be classified into two phases, prophase wherein the absolute value of acceleration increases and the anaphase wherein the absolute value of acceleration decreases.
Changing the equivalent mass according to such state (referred to as task process phase) during a series of movements makes it easier to perform the work, increases the work speed, reduces error, and reduces work load.
In a second aspect of the present invention, the work assist device includes a movable body for supporting a heavy article, an actuator for actuating the movable body, and a controller for adjusting the output of the actuator. The controller adjusts the actuator such that a force obtained by subtracting a resultant force of force proportional to acceleration of the heavy article, force proportional to speed, and force proportional to position value from force required for moving the heavy article with the same movement as that performed at that point. Also, coefficients proportional to acceleration, speed, and position value (the coefficient for position value is usually fixed at zero) are changed during the series of carrying work. Here, not all three types of coefficients need to be changed.
By providing the above-mentioned controller in the work assist device, a cooperation work is realized by an operator applying a resultant force of force proportional to the acceleration of the heavy article, force proportional to speed, and force proportional to position value. Further, the coefficients for making the force proportional to acceleration, speed, and position value (the coefficient for position value is usually fixed at zero) are changed during the series of carrying work. This makes it possible for the operator to continue work as if he were exchanging the assist devices having different mechanical properties. The operator is able to work using appropriate assist devices when dynamically and smoothly moving an article or when accurately moving an article by a small amount, resulting in a movement intended by the operator.
Here again, it is useful to change each coefficient according to the task process phases described earlier. It makes an operator feel as if he were selecting an appropriate assist device for each task process phase.
Here, it is extremely desirable that the changing pattern of coefficients proportional to acceleration, speed, and position value, is selectable according to one or more indexes including operator, work duration, experience, and state of fatigue of the operator.
For example, some operators are good at handling complicated works and some operators are good at handling speed-demanding works. Accordingly, the feeling with which one finds it easy to perform his work well differs between the operators. Also, the feeling with which one finds it convenient to perform his work well differs depending on the work duration and the state of fatigue of the operator. Therefore, by making it possible to select the changing pattern of the coefficient proportional to acceleration, coefficient proportional to speed, and coefficient proportional to position value, during carrying work, according to one or more of the indexes, the operator, work duration, experience, state of fatigue of the operator, an operator is able to work under various environments with a feeling which is convenient for performing his work well.